Removal of Pharmaceuticals from Aqueous Solutions by Photodegradation Using TiO2 and Sn/Zn/Fe-Doped TiO2 as Photocatalyst Under Ultraviolet and Visible Light

In this work, the photocatalytic degradation of amoxicillin (AMX), tetracycline(TCH), and diclofenac sodium(DCF) was studied using TiO₂ and Sn/Zn/Fe-doped TiO₂ as photocatalyst under ultraviolet (UV) and visible light. Photocatalysts were synthesized by sol–gel method and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR). Box–Behnken design (BBD) was used to achieve maximum %degradation by optimizing different parameters like the feed concentration (50–100 mg/L), feed pH (3–11), and the catalyst dosing (0.5–1.5 g/l). The study revealed that the Zn-doped TiO₂ photocatalyst (band gap of 3.23 eV) was the most effective which showed 90–95% degradation of all compounds within 90 min under UV radiation. Fe-doped TiO₂ (2.1 eV) and Sn-doped TiO₂(2.92 eV) showed the best results in the presence of visible light as it needs lower energy. To achieve maximum degradation efficiency under UV radiation, H₂O₂ (550 mL/L) was used along with Zn-doped photocatalyst under acidic conditions (at pH 3) for AMX, DCF, and basic conditions (at pH 11) for TCH. COD analysis was carried out before and after the experiment. COD removal efficiencies were found to be between 70–80% and liquid chromatography–mass spectrometry (LC–MS) analysis was performed to identify intermediate compounds formed during degradation.